How does the menstrual cycle affect a woman’s responses to exercise? Andrew Hamilton looks at recent research suggesting that women need to take extra care of their health and hydration status at certain times of the month MORE
Female athletes: take control of your body
Menstrual dysfunction among female athletes in hard training is surprisingly common, but undesirable for long-term health. Andrew Hamilton explains why and looks at research, which points to a possible a way forward…
Disordered eating in sport is an intractable problem in male and (particularly) female athletes, across a wide range of participation levels(1-6), In particular, the low calorie and nutrient content that result from a prolonged period of sub-optimum nutrition can give rise to a number of health problems. However, while recognized eating disorders such as anorexia nervosa, anorexia athletica and bulimia nervosa are sure-fire routes to nutritional and health problems, it’s important to appreciate that for female athletes at least, sub-optimum nutrition and health can easily arise, even when there’s no actual eating disorder present.
The female triad
To understand this, we need to appreciate the relationship between energy availability, menstrual function, and bone mineral density (BMD), which according to the American College of Sports Medicine defines the ‘female triad’(7). In very simple terms, the female triad describes how energy availability (dietary energy intake minus the energy required for exercise – ie the amount of dietary energy remaining for other body functions after exercise training) can impact negatively on menstrual function and consequently bone mineral density (see figure 1).
In particular, menstrual irregularity is worrying because of its negative impact on BMD. Irregular menstruation during adolescence has been associated with decreased BMD(8), and it is known that approximately 50% of peak bone mass is accrued during adolescence, which is a critical time to attain maximal bone mass(9). Abnormal menstrual function (menstrual dysfunction – MD) may manifest as oligomenorrhea (infrequent or very light menstruation) or amenorrhea (complete absence of menses). Changes in bone mineral density meanwhile are detectable using scanning techniques such as DXA, and may also present clinically as stress fractures, osteopenia, or osteoporosis. There’s also evidence that menstrual irregularity in athletes is associated with an increased risk of musculoskeletal injury(10,11).
Figure 1: Female athlete triad(7)
The far right of the spectrum represents optimum female health; the far left represents the female triad.
Energy demand and menstrual dysfunction
Compared to the general female population, studies have found a higher prevalence of abnormal menstrual function in the female athletic population(12-14). But while it’s true that there’s a higher prevalence of eating disorders among female athletes than the general female population, we need to understand that the high training loads and therefore energy demands of some female athletes can easily result in energy availability problems, even when eating patterns are ‘normal’.
As mentioned above, ‘energy availability’ is generally defined as the amount of dietary energy available for all physiological functions in the body once energy expenditure from exercise has been taken into account. In young healthy individuals, energy balance occurs at an energy availability of around 45kcals per kilo of free fatty mass per day. For example, suppose a 50kg female with 15% body fat has around 42.5kg of lean body mass. She would need 45kcals x 42.5 – ie around 1900kcals per day to achieve energy balance. By contrast, when energy availability falls to less than around 30kcals per kilo of free fatty mass per day, the reproductive function and bone formation are reduced to restore energy balance, resulting in an impairment of reproductive and skeletal health(15).
This deficit in energy availability of 15kcals per kilo of lean body mass equates to around 640kcals per day. This deficit can occur through simple calorie intake restriction – were our hypothetical female to go on a 1200kcal per day diet, she her body would undergo negative changes associated with the female triad and she would start to ‘move to the left’ on the triad spectrum (see figure 1). Another route is that she undertakes a training program, which involves expending 640+kcals per day – easily achieved by running 9 miles a day – and doesn’t increase her calorie count accordingly.
It’s also easy to see how some female athletes in sports such as gymnastics, ballet dancing, or figure skating, in which leanness and aesthetics are emphasized, are at greater risk of the female athletic triad; not only are they engaging in regular training, they may also develop poor nutritional behaviors such as food restriction, binging or purging etc in order to achieve what they perceive as an ideal body shape. Equally however, female endurance athletes undertaking large training volumes (eg triathletes) may often struggle to meet their energy requirements despite having very healthy eating behaviors.
Health implications of the female athletic triad
The health implications of the female athletic triad stem from the three key characteristics of the condition – an energy (calorie) deficiency, MD and reduced bone density and each of these is less than desirable.
*Energy deficiency – A short-term and mild energy deficiency does not normally present significant problems, especially if the diet is well balanced and nutrient rich. However, when energy deficits become larger and occur over longer periods of time, there are likely to be nutritional shortfalls (in addition to calories), which can lead to a variety of problems. These include decreased lean body mass, depleted glycogen stores, chronic fatigue, micronutrient deficiencies, anemia, dehydration, erosion of tooth enamel, gastrointestinal disorders or electrolyte and acid-base imbalances. Psychological problems, such as anxiety, depression or decreased self-esteem, may also occur, particularly after prolonged periods of undernutrition(16).
*Menstrual dysfunction – Menstrual cycle problems result from the suppression of the regular secretion of hypothalamic gonadotrophin-releasing hormone (GnRH), which in turn leads to a reduced secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), thus preventing ovarian stimulation, and causing a fall in the levels of estrogens and progesterone(17). When MD occurs, the resulting hormonal alterations can cause a number of complications; these include damage and inadequate repair of soft tissue, inhibition of immune and thyroid function, lost of the cardio-protective effects on lipids and vessel walls and changes in kidney function(18). In addition, lack of stimulation of oestrogen receptors in blood vessels can result in impaired endothelium-dependent arterial vasodilation(19,20).
*Bone health – Exercise is beneficial for bone health since it encourages greater bone mineralization, leading to increased BMD and therefore higher bone strength. However, female athletes with MD tend to have significantly lower BMDs than those with who don’t (21); the factors contributing to MD can therefore put athletes at risk for compromised bone health and for the development of abnormally low BMD (osteopenia) and osteoporosis(22). The big risk for athletes suffering from reduced BMD is stress fracture. Although the incidence of stress fracture is also influence by other factors such as age, prior exercise training and alcohol consumption, studies show that female athletes suffering the female triad are especially at risk(23) The most common site of stress fractures in female athletes is the tibia, accounting for 25% to 63% of cases(24). Alarmingly, the effects of diminished BMD as a result of the female triad appear to be very persistent – to date no long-term study has demonstrated that lost BMD can be fully regained even when athletes regain their normal reproductive status. Moreover, because peak bone mass is reached by the third decade of life, the problem of diminished BMD is especially critical for adolescent athletes(25).
Overcoming menstrual dysfunction
To date, much of the focus has centered on the detection and treatment of eating disorders, which are common among female populations. However, athletes in heavy training may struggle to attain a sufficient energy balance even with excellent eating habits. When eating disorders are present, this becomes an almost impossible task.
Many of the early eating disorder prevention programs have typically consisted of psychological and educational interventions; unfortunately however, research generally indicates that while this type of intervention is effective at increasing knowledge about the problem, it is substantially less effective at actually changing eating behaviors(26,27). In more recent years, eating disorder prevention programs have improved and programs with good empirical support are the cognitive dissonance-based prevention (DBP) and the Healthy Weight Prevention Intervention (HWPI) programs(28, 29).
Despite the positive findings from the DBP and HWPI approaches to combating eating disorders, the problem is that neither has been properly tested on athletes – a population that may be particularly resistant to making changes in eating behavior. Another consideration of course is that many female athletes who suffer from MD do not have an eating disorder as such – rather they simply struggle to consume sufficient energy for their needs.
A nutritional approach
Since many female athletes with MD don’t suffer from eating disorders, and that in those who do, strategies to help are far from guaranteed to work, an obvious question to ask is whether there are any other, better approaches that may be useful? Back in the late 90s, researchers looked into a diet and exercise training intervention program designed to improve energy balance and nutritional status in four amenorrheic athletes(30). In particular, they wanted to see whether the intervention could reverse the athletes’ amenorrhea. The 20-week program provided a daily sport nutrition supplement, which boosted calorie intake by 360kcals per day, and asked the athletes to take an extra day of rest per week. The results showed that menses and ovulation was restored in three of the four athletes – an encouraging finding.
The problem is of course that many female athletes and/or their coaches are (quite naturally) reluctant to add rest days to their training programs. However, a 2013 case study on two female athletes makes for further interesting reading (31). Two athletes with amenorrhea were chosen to investigate the impact of increased calorie intake on recovery of menstrual function and bone health. One participant (amenorrhea for 3 months) was 19 years old and had a body mass index (BMI) of 20.4kg/m2 at baseline. She increased her calorie intake by 276kcals per day (13%), on average, during the intervention, and her body mass increased by 4.2kg (8%). The second participant (amenorrhea for 11 months) was 24 years old and had a BMI of 19.7 kg/m2. She increased her caloric intake by 1,881kcals per day (27%) and increased body mass by 2.8 kg (5%). Figure 2 shows how her reproductive hormones changed over the intervention period. Resumption of menses occurred 23 and 74 days into the intervention for the women with short-term and long-term amenorrhea, respectively, and the onset of ovulation and regular cycles corresponded with changes in body weight. Another observation was that while no increases in BMD were observed in the two athletes, P1NP, a marker of bone formation, increased by around 50% in both subjects.
Figure 2: Change in reproductive hormone levels in subject #2
Red trace shows levels of E1G – a key marker of oestrogen, low levels of which are strongly implicated in MD.
The case study above suggests that simply adding energy to the diet in a supplement form could be enough to help return amenorrheic athletes back to a normal menstrual cycle, without the need for additional rest. However, a case study cannot provide strong enough scientific evidence upon which to draw solid conclusions. But a study by US scientists suggests that this approach is indeed a valid one(32).
The researchers investigated whether a 6-month carbohydrate-protein supplement providing 54g of carbohydrate and 20g of protein (360kcals) per day could improve energy status and restore menses in eight female athletes suffering from MD. Before and after the intervention, reproductive and thyroid hormones, bone health (BMD, bone mineral content, bone markers), muscle strength/power and protein metabolism markers, profile of mood state (POMS), and energy intake/energy expenditure from 7-day food & activity records were measured.
The results showed that in terms of bone health, muscular strength/power and hormone balance, there were no significant changes. What was striking however was that all of the athletes resumed their menses, taking on average 2.6 months to first menses (3.5 cycles). Another interesting observation was that athletes who had been amenorrheic for 8 months or longer took significantly longer to resume menses than those amenorrheic for less than 8 months. As a side note, spinal region BMDs in the over-8 month group were also significantly lower than the under 8-month athletes. A further finding was that POMS depression scores improved by 8% as a result of the intervention. The significance of these findings is that this study is the first to demonstrate that when athletes suffering from MD consistently consume an extra 360kcals per day for 6-months, normal menses can be restored even though normal exercise training is continued. As such, this approach could prove a very useful tool for helping female athletes who suffer from exercise-related MD.
MD (with its associated implications for health) is surprisingly common in female athletes. A root cause is insufficient calorie intake to meet the demands of training. This may be as a result of an eating disorder, but many athletes with perfectly healthy eating habits can suffer from abnormal menses simply because of the high volumes of training (and therefore energy expended) they undertake. Eating disorder intervention/prevention programmes are of undoubted value where an eating disorder is present. However, restoring energy balance remains critical, which is where nutritional intervention appears to be extremely useful – to all athletes who struggle to meet their energy needs whatever the reason. Although more studies are still needed, the latest research suggests that consuming a daily carbohydrate and protein supplement containing around 360kcals with around 2.5 parts of carbohydrate to one part of protein could be an extremely effective intervention to normalise the menstrual cycle, with all the health benefits that brings to the female body.
- Clin J Sport Med. 2004 Jan;14(1):25-32
- American Psychiatric Association: “Diagnostic and Statistical Manual of Mental Disorders” (DSM-IV-TR), 4th Edition, June 2000
- Int J Sports Med. 2007 Apr;28(4):340-5
- Nutrition 2009 Jun;25(6):634-9
- Med Sci Sports Exerc. 2003 May;35(5):711-9
- Phys Ther Sport. 2011 Aug;12(3):108-16
- Med Sci Sports Exerc; 2007;39(10):1867-1882
- Bone. 2007;41(3):371-377
- Arch Pediatr Adolesc Med. 2006; 160(1 0): 1026-1 032.
- Clin J Sport Med. 2000; 10(2): 110-116
- Am J Physiol Endocrinol Metab. 2005;289(3):E373-E381
- Int J Sport Nutr Exerc Metab. 2002;12(3):281-293
- Clin J Sport Med. 2009;19(5):421-428
- Acta Obstet Gynecol Scand. 2007;86(1):65-72
- J Sport Sci 2007; 25: S67-S71
- J Sport Sci 2007; 25: S67-S71
- Exerc Sport Sci Rev 2003; 31:144-8.26
- Curr Sports Med Rep 2007; 6: 397-404(
- PM R 2011; 3: 458-65
- Clin J Sport Med 2011;21: 119-25
- Bone 2009; 45: 104-9
- Perform Enhanc Health 2012; 1: 10-27
- Orthop Clin North Am 2006; 37: 575-83
- Am J Sports Med 2006; 34: 108-15
- Clin J Sport Med 2004; 14: 25-32
- Psychological Bulletin. 2004; 130:206–227
- Annual Review of Clinical Psychology. 2007; 3:207–231
- Prevention Science. 2008; 9:114–128
- J Consulting Clin Psychology. 2008; 76:329–34
- Int. J. Sport Nutr. 1999, 9, 70–88
- J. Int. Soc. Sports Nutr. 2013, 10, 34
- Nutrients 2014, 6, 3018-30